I'm just wondering why frozen fruit, more specifically frozen berries take so long to defrost in the refrigerator?

I bought some frozen berries (in bag) and placed them in the fridge overnight. They were out of the freezer for at least 12 hrs -- and the next morning they were still frozen. The fridge temp was 40f. So anyway, then I remove the berries from the bag and just place them on a plate.
4 hrs later they are STILL partially frozen. What's going on here? My goal is to put them on a pound cake with some whipped cream on top-- but at this rate, it'll be ready about a yr from now. Why do frozen berries stay frozen for so long?

Berries frozen in the bag will usually clump together and thus present a smaller surface area compared to its mass. This is why crushed ice melts more quickly than cubed ice.

Secondly, frozen berries will not act like pure water and will melt more slowly; I would wager that the berries have a much lower thermal conductivity.posted by Optimus Chyme at 7:00 AM on March 24, 2006

Also, the best way to quickly unfreeze items like berries or frozen shrimp or the like is to put them in a sealed bag and run cold - not hot - water over them.posted by Optimus Chyme at 7:02 AM on March 24, 2006

There's more, sorry - the reason that things take a long time to defrost just sitting in the fridge goes back to thermal conductivity. Air conducts heat very slowly. There's just not that many particles to transfer heat with. Water is much more dense and has far more particles by volume. It's why good thermoses have a vacuum sealed area and why icy comets don't melt in space.posted by Optimus Chyme at 7:07 AM on March 24, 2006

O.C. is right... the best way to defrost anything, in fact, is to run cold water over it. I place a large bowl in the sink, set the food in it (sealed of course) and turn on the cold water to a point where it isn't making an annoying whining or dribbling noise and let 'er rip. The refrigerator method is fine if you're not expecting to use the food in the next couple of days.posted by Witty at 7:13 AM on March 24, 2006

Also, the best way to quickly unfreeze items like berries or frozen shrimp or the like is to put them in a sealed bag and run cold - not hot - water over them.

Hot water will defrost the items quicker, but it is recommended that you use cold water for reasons of food safety.posted by skwm at 7:30 AM on March 24, 2006

Plus, it will start the "cook" or poach the food. Not good. The water doesn't have to be ice cold, but no more than body temperature in my opinion.posted by Witty at 7:34 AM on March 24, 2006

Another reason defrosting in the fridge takes so long is that your fridge is only 8 degrees F above freezing. That's not much of a temperature gradient - there's not a whole lot of thermal energy in the fridge to defrost the fruit.posted by Geektronica at 7:14 PM on March 25, 2006

I hope our answers were comprehensive and helpful and that your pound cake turned out okay.posted by Optimus Chyme at 7:43 AM on March 26, 2006

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